Magnetic system for amplifying cathode ray deflection



April 19, 1966 C. ZLOTYKAMIN ETAL MAGNETIC SYSTEM FOR AMPLIFYING CATHODE RAY DEFLECTION Filed July 12, 1962 INVENTOR CHARLES ZLOTYKOMIN ANDRE GUILLAUME AGENT United States Patent 5 Claims. (or. sis-71 The invention relates to a cathode-ray oscillograph in which the deflection of an electron beam under the infiuence of a signal voltage, particularly in the form of a short pulse or of high-frequency pulses, applied to a pair of deflecting plates between which the said beam passes or applied to an equivalent deflecting member, for example a wave propagation line, is observed. It should, however, be understood that the invention is not limited to cathode-ray oscillographs but relates to any similar apparatus in which the deflection of an electron beam is observed or utilized.

In the case to be discussed more particularly hereinafter and. which has led to the invention, the signals to be applied to the cathode-ray oscillograph are very short or have a very high frequency and are weak. They cannot readily be amplified beforehand and are then liable to be distorted before being applied to the cathode-ray oscillograph. Therefore it has already been proposed (see, for example, British patent specification 650,044 filed September 9th, 1947) to increase the deflection of the beam, which deflection is obtained with the aid of two electromagnetic systems, by the provision behind them (that is to say when following the path of the electrons) of a particular electromagnetic system forming a lens. Thus the sensitivity (which may be defined by the number of centimeters of the deflection measured on the screen divided by the voltage in volts between the electrostatic deflecting plates or equivalent system may be increased without reducing the image height (=deflection of a spot on the screen).

However, the solution proposed in the said patent specification employs a non-uniform magnetic field the direction of which on one side of the axis is opposite to its direction on the other side, and it suffers from the drawback that, when the sensitivity is increased in one direction, it is proportionally decreased in the direction at right angles thereto.

It is the object of the invention to provide a cathoderay oscillograph or similar apparatus which satisfies the various practical requirements better than has been the case hitherto and especially to avoid the above mentioned drawback. Further it permits the manufacture of an oscillograph the sensitivity of which is variable at will.

It consists mainly in that, in a cathode-ray oscillograph electrons behind the deflecting systems and in order to amplify this deflection a member producing a transverse magnetic field in a region through which the electrons must pass, the said member, which may be constituted by several separate parts, is arranged so as to produce several partial regions in each of which a uniform magnetic field prevails through which the electrons must pass, and so that the entry boundary of each region is oriented at right angles or substantially at right angles to the mean direction of the axis of the beam impinging on the said boundary.

More particularly a pair of opposite pole pieces (or a pair of equivalent energised solenoids) with rectangular cross-section provides a non-limitative simple example, which will be explained more fully hereinafter, of such a device producing a uniform magnetic field the entry 3,247,409 Patented Apr. 19, 1966 plane of which must be substantially perpendicular to the axis of the electron beam to enable the arrangement to function correctly.

According to a more elaborate embodiment use may also be made of at least two sets of such pairs of pole pieces which in this case are advantageously caused to produce, as will be discussed hereinafter, the uniform magnetic fields of opposite directions through which the electrons pass successively, provided that the entry planes are also substantially perpendicular to the mean electron beam, which implies that the second pair of pole pieces should make a marked angle with the direction of the beam issuing from the electron gun.

In addition to the above mentioned main arrangement the invention consists of various other arrangements which may be used separately or preferably simultaneously and which will be explained more fully hereinafter.

The invention relates to certain embodiments and applications (especially for high-frequency oscillograms) and as novel industrial products to cathode-ray oscillo graphs in which the above mentioned arrangements are used, to the components and special tools used in their manufacture and to the fixed or movable units comprising such cathode-ray oscillographs.

Without Wis-hing thereby to limit the invention, the latter will now be explained more particularly with reference to the accompanying drawing, in which:

FIG. 1 shows the shape of an electron beam passing through a magnetic field,

FIG. 2 shows an arrangement in accordance with the invention;

FIG. 3 shows another arrangement in accordance with the invention.

It is assumed that an electron beam passes through a rectangular space of width a in which prevails an induced uniform transverse magnetic field B (FIG. 1). A beam p assumed to be infinitely thin is inclined through an angle of incidence 0 with respect to the normal to the large side of a rectangle P which also represents a crosssection of the pole piece producing the field B. A beam influenced by this field describes a circular arc of radius R and emerges at a different angle I' with respect to the normal on the rear plane so that:

where ere v is the velocity of the electron, e its charge and In its mass. From this it follows that:

When 0 is near Zero (cos 0=I, sin 0*--O), which is the practical case under consideration, d I /d0 exceeds unity and approximates to l/cos l' Thus there is provided an amplification of the angular variation of the beam and hence of the deflection (that is to say, an increase in the sensitivity), however, a mean deflection I is superimposed.

For example with a=1 cm., B=200 gauss, V=4000 volts (accelerating voltage), then I' =72 and the gain is Other more or less complicated shapes of the boundary curve of the magnetic field are possible. They all have to satisfy the condition that:

However, the mean deflection I is troublesome for it involves a complicated structure of the apparatus (because of the deviated form of the beam) and furthermore there is no possibility of readily varying the angle of deflection. Hence, according to the invention there is preferably provided not a single magnetic system, but two such systems arranged one behind the other in the path of the electrons, the second system producing a magnetic field opposite to that of the first.

FIG. 2 shows schematically (the evacuated envelope is not shown and the electrodes are shown diagrammatically) that the second magnetic system (pole piece P) produces a field of the same absolute strength and of opposite direction through the same distance a, the pole piece P being inclined through an angle I In this case it may be assumed, when the initial deflec tion is slight, that the entry plane of P is perpendicular to the axis of the electron gun, but this does not apply to the entry plane of P. Thus the beam emerges parallel to its first incidence on P, that is to say substantially parallel to the axis of the arrangement but with further improved sensitivity; the overall gain is l/cos P It should be noted that this disposition of the two. pole pieces one behind the other so as to return the beam to a direction parallel to its first incidence should be distinguished from that shown, for example, in FIG. 2 of French patent specification 866,058 of February 28, 1940, in which also two magnetic systems are shown which act successively on an electron beam. In the said specification the two magnetic systems are used to provide the circular movement of the spot on the analysing screen by a variable initial deflection, whereas in the apparatus in accordance with the invention the (already provided electrostatic) initial deflection is amplified by the magnetic devices according to the invention.

Therefore, whereas the magnetic devices described in the said specification are both perpendicular to the axis of the apparatus, the second magnetic device is inclined through the angle I with respect to the beam emerging from the deflecting system.

In general, if n identical magnetic deflecting systems are used, the gain in sensitivity is:

The number n preferably is even to obtain an output beam parallel to the axis of the electron gun.

In the above described example there is obtained a gain in the angle of deflection; the same gain is obtained in the maximum image height, other things remaining the same. This means that a gain:

(cos I' Zn in the product of the sensitivity times the maximum image height is obtained. Due to the said system one may, for example, vary the spacing of the deflecting plates D forming lenses in the vertical and horizontal planes. Suitable different voltages are applied to these electrodes in order to control the focussing of the beam independently in the two planes.

In FIG. 3 the deflection produced by the second magnetic system is such as to bring the point I in which the beam impinges on the screen into the axis of the gun (while in FIG. 2 the beam impinged at 1'). However, the desired increase in sensitivity is obtained in this manner also. Although the second field produced by an electromagnet remains uniform in the region in which it is produced, it is for this purpose varied as a function of the first, for example, with the aid of a manually operated rheostat or any other means; the spacing of the pole pieces P and P may also be varied. The two pairs of pole pieces may also be constituted by electromagne-ts, their fields being controlled progressively. Thus an oscillograph with variable sensitivity is obtained, which may be valuable in certain applications.

With respect to the variable sensitivity of the apparatus it will be appreciated that the electron beam cannot always be absolutely at right angles to the entry plane of P.

Therefore it is advantageous for the length of the pole pieces P to be greater than that of the pole pieces P, as is shown in FIG. 3, so that the path of the electrons may be influenced even when the increase in sensitivity is slight.

The invention is not limited to the embodiments described hereinbefore and/ or illustrated and includes any modification thereof.

What is claimed is:

1. A cathode-ray oscillograph comprising a deflection system, a screen, a first magnet system for producing a first transverse magnetic field in a region through which electrons moving in a given path have to pass, and a second magnet system for producing a second transverse magnetic field having a direction opposite that of the first field in a second region through which the electrons have to pass after passing through the first region, each of said magnet systems comprising a pair of substantially rectangular pole-pieces, the larger dimension of the pole-pieces or the first magnet system being substantially perpendicular to the path of the electrons, the larger dimension of the pole-pieces of the second magnet system forming an angle other than 90 with an axis parallel to an extension of the path of the electrons entering the first region.

2. A cathode-ray oscillograph comprising a deflection system, a screen, a first magnet system for producing a first transverse magnetic field in a region through which electrons moving in a given path have to pass, and a second magnet system for producing a second transverse magnetic field having a direction opposite that of the first field in a second region through which the electrons have to pass after passing through the first region, each 7 of said magnet systems comprising a pair of substantially rectangular pole-pieces, the larger dimension of the polepieces of the first magnet system being substantially perpendicular to the path of the electrons, the larger dimension of the pole-pieces of the second magnet system forming an angle other than 90 with an axis parallel to an extension of the path of the electrons entering the first region, said second magnet system producing a magnetic field having a strength greater than that produced by the or an equivalent parameter of the deflecting system so i as to retain a moderate maximum image height while still further increasing the sensitivity.

Since the beam is focusedonto the screen E it shows a certain convergence. This convergence will also be amplified in the plane of the drawing (referred to, for example, as vertical plane) by the arrangement according to the invention withoutbeing modified in the horizontal plane. Thus astigmatism of the spot is introduced.

To obviate this difficulty, according to the invention the focussing electrode, which usually is a body of revolution, is replaced by two systems of electrodes H and V first field whereby electrons are converged to the point of intersection of the path and the screen.

3. A cathode-ray oscillograph comprising a deflection system, a screen, a first permanent magnet system for producing a first transverse magnetic field in a region through which electrons moving in a given path have to pass, and a second permanent magnet system for producing a second transverse magnetic field having a direction opposite that of the first field in a second region through j which the electrons have to pass after passing through the first region, each of said magnet systems comprising a pair of substantially rectangular pole-pieces, the larger dimension of the pole-pieces of the first magnet system being substantially perpendicular to the path of the electrons, the larger dimension of the pole-pieces of the second magnet system forming an angle other than 90 with an axis parallel to an extension of the path of the electrons entering the first region.

4. A cathode-ray oscillogr-aph comprising a deflection system, a screen, a first magnet system for producing a first transverse magnetic field in a region through which electrons moving in a given path have to pass, and a second magnet system for producing a second transverse magnetic field having a direction opposite that of the first field in a second region through which the electrons have to pass after passing through the first region, each of said magnet systems comprising a pair of substantially rectangular pole-pieces, the larger dimension of the polepieces of the first magnet system being substantially perpendicular to the path of the electrons, the larger dimension of the pole-pieces of the second magnet system forming an angle other than 90 with an axis parallel to an extension of the path of the electrons entering the first region, each of said magnet systems fiurther comprising means to vary the field strength thereof.

5. A cathode-ray oscillograph comprising a deflection system, a screen, a first magnet system for producing a first transverse magnetic field in a region through which electrons moving in a given path have to pass, and a second magnet system for producing a second transverse magnetic field having a direction opposite that of the first field in a second region through which the electrons have to pass after passing through the first region, each of said magnet systems comprising a pair of substantially rectangular pole-pieces, the larger dimension of the pole-pieces of the second magnet system forming an angle other than 90 with an axis parallel to an extension of the path of the electrons entering the first region, each of said magnet :systems further comprising electromagnets, and means to control the energization thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,185,138 12/1939 Wolif 31379 X 2,454,345 11/ 1948 Rudenlberg 31379 2,944,174 7/ 1960 Taylor 3l379 X GEORGE N. WESTBY, Primary Examiner. ROBERT SEGAL, Examiner. 

1. A CATHODE-RAY OSCILLOGRAPH COMPRISING A DEFLECTION SYSTEM, A SCREEN, A FIRST MAGNET SYSTEM FOR PRODUCING A FIRST TRANSVERSE MAGNETIC FIELD IN A REGION THROUGH WHICH ELECTRONS MOVING IN A GIVEN PATH HAVE TO PASS, AND A SECOND MAGNET SYSTEM FOR PRODUCING A SECOND TRANSVERSE MAGNETIC FIELD HAVING A DIRECTION OPPOSITE THAT OF THE FIRST FIELD IN A SECOND REGION THROUGH WHICH THE ELECTRONS HAVE TO PASS AFTER PASSING THROUGH THE FIRST REGION, EACH OF SAID MAGNET SYSTEMS COMPRISING A PAIR OF SUBSTANTIALLY RECTANGULAR POLE-PIECES, THE LARGER DIMENSION OF THE POLE-PIECES OF THE FIRST MAGNET SYSTEM BEING SUBSTANTIALLY PERPENDICULAR TO THE PATH OF THE ELECTRONS, THE LARGER DIMENSION OF THE POLE-PIECES OF THE SECOND MAGNET SYSTEM FORMING AN ANGLE OTHER THAN 90* WITH AN AXIS PARALLEL TO AN EXTENSION OF THE PATH OF THE ELECTRONS ENTERING THE FIRST REGION. 